2,6-Difluoroaniline is useful as an intermediate in the manufacture of a variety of chemical products including, for example, dyes, pharmaceuticals and agricultural chemicals, and is presently manufactured in a multistep process involving the following reaction sequence: ##STR1##
i) ammoxidation of 2,6-dichlorotoluene to 2,6-dichlorobenzonitrile;
ii) halogen-exchange to 2,6-difluorobenzonitrile;
iii) hydration to 2,6-difluorobenzamide; and
iv) Hoffman rearrangement to 2,6-difluoroaniline.
In addition, 2,6-dichlorotoluene itself is not readily available. Thus, as a result of the complexities of the chemistry, although commercially available, 2,6-difluoroaniline is quite expensive.
Alternative technologies have been suggested to manufacture 2,6-difluoroaniline, but they also have serious drawbacks. For example, fluorinated aromatics are often prepared by diazonium chemistry in which an amino moiety is transformed into a fluorine substituent by reaction with nitrous acid to form a diazonium salt and subsequent decomposition of the diazonium salt in the presence of fluoride. However, diazonium salts are unstable and the decomposition reaction is highly exothermic. In addition, the decompositions are generally conducted in highly reactive and corrosive anhydrous hydrofluoric acid.
Alternatively, 2,6-difluoroaniline has also been prepared via lithiation of 1,3-difluorobenzene followed by carbonation to the carboxylic acid and conversion of the acid moiety to the amine with hydrazoic acid (see British Patent 1,080,167). Unfortunately, neither lithiation nor hydrazoic acid lend themselves to large scale use.
Thus, it is desirable to have a process for safely and economically producing 2,6-difluoroaniline in good yield from readily available starting materials.